The invention relates to a transmission system for transmitting a multiplex signal from a transmitter to a receiver, said receiver comprising storage means for storing data sections included in the multiplex signal in dependence on information present in the multiplex signal.
The invention further relates to a transmitter for transmitting a plurality of multiplex signals, a receiver for receiving a multiplex signal, storage means for storing data sections included in a multiplex signal and a multiplex signal comprising data sections and therewith corresponding storage information.
A transmission system according to the preamble is known from EP-A 0 827 340. In modem digital broadcast systems a transmitter, e.g. a headend, typically transmits a large number of services (or channels) to a plurality of receivers, like for instance television sets or set-top boxes. Such a service can contain an audio/video stream, an interactive application (for example in the MHEG-5 format), other kinds of data or a combination of these elements. An MPEG-2 transport stream is a multiplex of a number of services. Typically, a transmitter transmits several transport streams to the set-top boxes. A set-top box can tune to a specific transport stream and is then able to retrieve information from the transport stream. Such a set-top box typically has only one tuner and is thus merely able to receive one single transport stream at a time. When amuser wants to look at a television program, or wants to run an interactive application, or wants to access other kinds of data the set-top box or television set tunes to the corresponding transport stream and retrieves and processes the required data from the service as it is being broadcast at that moment.
Interactive applications, like for instance tele-banking, tele-shopping or an electronic newspaper are typically broadcast in a carousel-like fashion, i.e. the therewith corresponding data sections are repeated periodically in the transport stream. For instance, both DVB and DAVIC have specified DSM-CC object carousels for broadcasting interactive applications. The response time of this kind of applications can be improved considerably by applying some kind of caching in the set-top box, i.e. storing data sections in the set-top box which may have to be accessed in the future. Otherwise, if caching is not used and the set-top box wants to retrieve a part of the interactive application, the set-top box must wait until that particular part is broadcast again, In order to be able to cache data, the set-top box must have access to a storage device like for instance a hard disk. The set-top box can also use this storage device to store linear television content, like for instance short news bulletins or weather forecasts. These programs can be viewed by the user whenever this is convenient.
Not all information is equally important to cache. So, in order for a set-top box to be able to decide on what data to cache, it should know the relative cache priorities of cacheable data. A service provider may want to set these cache priorities and broadcast them to the set-top boxes.
In the known transmission system a transport stream is broadcast by a transmitter to a number of receivers. This transport stream comprises a number of services which are embedded into a single interactive application. The transport stream further comprises cache priorities for data sections corresponding with the application and the services. These cache priorities can be used by the receivers to cache the data sections so that a desired piece of image information is displayed immediately upon a request of a user.
An object of the invention is to provide a transmission system, wherein the receiver or set-top box is able to efficiently handle the caching of a plurality of services, which services are not embedded into a single application. This object is achieved in the transmission system according to the invention, which is characterized in that the information for the multiplex signal is contained in a single information section. By concentrating the cache priorities for all services included in the transport stream into a single information section, e.g. a DVB SI table, the set-top box can quickly get a complete view of all cacheable data included in the transport stream by simply reading this information section.
An embodiment of the transmission system according to the invention is characterized in that the transmission system is embodied so as to transmit at least one further multiplex signal from the transmitter to the receiver, whereby the information section also contains the information for the further multiplex signal. By concentrating the cache priorities for all services included in a plurality of transport streams transmitted by the transmitter into a single information section, the set-top box can quickly get a complete view of all cacheable data included in these transport streams simply by reading this information section. In this way, there is no need for the set-top box to tune to all the transport streams sequentially in order to obtain a complete overview of the cache priorities. It suffices to only tune to a transport stream which includes the complete overview in a single information section.